I think it just requires enough puddle that someone would say “what’d you do, piss yourself?”. The feedback isn’t required, but that’s the bar for it. Sprinkles, post pee seepage splatterback or even being a uncontrollable fire firehouse wouldn’t really constitute pissing yourself. I’ll go one further and make the distinction of intent. Even if you are trying to be outside the ‘ole trousers and you pee a gallon on your front pleats and down to your knee, you’d say you pissed all over yourself, not pissed yourself.